How Bulk Binds Improve Performance

The assigning of values to the PL/SQL variables in SQL statements is known as binding.

The binding of the whole collection at once is known as the bulk binding. The Bulk binds improve performance by minimizing the number of the context switches between the PL/SQL and SQL engines. With the bulk binds, whole collections, not just an individual element, are passed back and forth. For illustration, the DELETE statement below is sent to the SQL engine just once, with the whole nested table:

DECLARE

TYPE NumList IS TABLE OF NUMBER;

mgrs NumList := NumList(7566, 7782, ...); -- manager numbers

BEGIN

...

FORALL i IN mgrs.FIRST..mgrs.LAST

DELETE FROM emp WHERE mgr = mgrs(i);

END;

In the illustration below, 5000 part numbers and names are loaded into the index-by tables. Then, all the table elements are inserted into a database table twice. At First, they are inserted using a FOR loop, that completes in 38 seconds. Then, they are bulk-inserted by using a FORALL statement that completes in only 3 seconds.

SQL> SET SERVEROUTPUT ON

SQL> CREATE TABLE parts (pnum NUMBER(4), pname CHAR(15));

Table created.

SQL> GET test.sql

1 DECLARE

2 TYPE NumTab IS TABLE OF NUMBER(4) INDEX BY BINARY_INTEGER;

3 TYPE NameTab IS TABLE OF CHAR(15) INDEX BY BINARY_INTEGER;

4 pnums NumTab;

5 pnames NameTab;

6 t1 CHAR(5);

7 t2 CHAR(5);

8 t3 CHAR(5);

9 PROCEDURE get_time (t OUT NUMBER) IS

10 BEGIN SELECT TO_CHAR(SYSDATE,'SSSSS') INTO t FROM dual; END;

11 BEGIN

12 FOR j IN 1..5000 LOOP -- load index-by tables

13 pnums(j) := j;

14 pnames(j) := 'Part No. ' || TO_CHAR(j); 15 END LOOP;

16 get_time(t1);

17 FOR i IN 1..5000 LOOP -- use FOR loop

18 INSERT INTO parts VALUES (pnums(i), pnames(i));

19 END LOOP;

20 get_time(t2);

21 FORALL i IN 1..5000 -- use FORALL statement

22 INSERT INTO parts VALUES (pnums(i), pnames(i));

23 get_time(t3);

24 DBMS_OUTPUT.PUT_LINE('Execution Time (secs)');

25 DBMS_OUTPUT.PUT_LINE('---------------------');

26 DBMS_OUTPUT.PUT_LINE('FOR loop: ' || TO_CHAR(t2 - t1));

27 DBMS_OUTPUT.PUT_LINE('FORALL: ' || TO_CHAR(t3 - t2));

28* END;

SQL> /

Execution Time (secs)

---------------------

FOR loop: 38

FORALL: 3

PL/SQL process successfully completed.

In the bulk-bind input collections, you can use the FORALL statement. And in the bulk-bind output collections, you can use the BULK COLLECT clause.